Bladder cancer is the fourth most common cancer (excluding nonmelanoma skin cancer) among American men. The development of bladder cancer may in part relate to the direct effects of carcinogenic compounds in the urine on the bladder mucosa. A high consumption of fluids may reduce such exposure by diluting the urine and by reducing the duration of exposure because of an increased frequency of urination. Michaud and colleagues examined the relationship between fluid intake and bladder cancer in men participating in the Health Professionals Follow-up Study.

This large-scale study began in 1986 and initially included 51,529 men aged 40 through 75 years who responded to the questionnaire mailed to them. Follow-up questionnaires were subsequently mailed during the 10-year study. A total of 47,909 men were eligible for follow-up.

The questionnaire included queries on dietary intake and the consumption of 22 different beverages, such as water, milk, juice, coffee and alcohol. Other information obtained from the questionnaire included the person's medical history, smoking history, exercise habits, height, weight and use of medications. A diagnosis of bladder cancer was confirmed by review of the medical records, information from a family member if necessary and review of the pathology report, which was available in 90 percent of the patients.

A total of 252 cases of bladder cancer occurred in the study population. Advanced age and smoking were found to have the strongest correlation with bladder cancer. Compared with men who never smoked, men with 65 or more pack-years of smoking were 3.7 times more likely to have cancer. With respect to age, the relative risks of bladder cancer were 5.6 in men aged 70 through 74, 6.2 in those aged 75 through 79 and 11.6 in those aged 80 or older.

In the age-adjusted analysis of the data, daily total fluid intake reported in 1986 was inversely associated with a risk of bladder cancer. The relative risk for the highest quintile of fluid intake (greater than 2,531 mL per day) was 0.51, compared with the lowest quintile (less than 1,290 mL per day). Sixty-one cases of bladder cancer occurred among men reporting a daily fluid intake of less than 1,290 mL. In contrast, 33 cases occurred in men reporting a daily fluid intake in excess of 2,531 mL. For daily fluid intakes between these two extremes, the incidence of bladder cancer was 54 cases in men who drank 1,290 to 1,674 mL of fluid daily, 57 cases in those with a daily fluid intake of 1,675 to 2,050 mL and 47 cases in those with a daily fluid intake of 2,051 to 2,531 mL.

Other than water, no specific beverage had a statistically significant association with the risk of bladder cancer. Men who drank more than 1,440 mL (six or more cups) of water daily had a 51 percent reduction in bladder cancer risk compared with the risk in men who drank less than 240 mL (1 cup) of water per day. No association was found between an increased risk of bladder cancer and intake of caffeine-containing beverages, specifically coffee and tea.

The authors conclude that a high daily intake of fluids is associated with a reduced risk of bladder cancer. The risk reduction was 7 percent for every 240-mL increment of daily fluid intake. Unlike previous studies, the current study did not reveal an increased risk of bladder cancer among men who consumed alcohol or coffee. In view of the findings from this study, the authors recommend a generous daily intake of fluids because a high fluid intake appears to reduce the risk of bladder cancer.